The present invention relates to a method for welding a sphere onto a metal sheet.
The use of spheres or spherical geometry and, additionally or optionally, spheroidal geometry, as joining elements or fastening elements in the construction of motor vehicle bodies is already known from earlier patent applications, some of which are not prior publications. An essential condition for an industrialization of this production method lies in the success of connecting in an automated way the corresponding spherical or spheroidal bodies to a metal sheet as precisely and reliably as possible.
The object of the invention is to provide a method, in particular an automated method, that is configured for connecting a sphere to a metal sheet and that makes it possible to achieve a high degree of positioning accuracy and a high joint strength.
This and other objects are achieved by providing a method for welding a sphere onto a metal sheet, the method comprising the acts of: providing a sphere; providing a first electrode; picking up the sphere by use of the first electrode; providing a metal sheet; providing a second electrode; pressing the metal sheet and sphere together in such a way that the sphere is pressed against the metal sheet by the first electrode and that the metal sheet is pressed against the sphere by use of the second electrode; and welding the sphere and the metal sheet together by generating a welding current between the first and second electrodes.
The basic idea of the invention consists of connecting the sphere to the metal sheet by resistance welding. Resistance welding enables short cycle times and a high degree of positioning accuracy.
This method makes it possible to position the sphere with a high degree of accuracy. An additional advantage lies in the fact that this method produces hardly any welding splatter, as compared to other welding methods, so that this method facilitates a clean, high quality, joint made by welding.
The method according to the invention provides that a sphere that is to be welded onto a metal sheet is picked up by means of a first electrode. In the next step, the metal sheet and the sphere are pressed together. In this context the sphere is pressed against the metal sheet by way of the first electrode, and the metal sheet is pressed from the backside of the metal sheet against the sphere by way of a second electrode, so that the result is a buildup of a defined contact pressure. Finally, the sphere is connected to the metal sheet by welding in a step that lasts a few fractions of a second, in that a welding current, which flows through the metal sheet and the sphere, is generated between the two electrodes.
It can be provided that the welding current is generated for less than one second, in particular for less than 60 ms, and more particularly for less than 10 ms.
According to a further aspect of the invention, the welding current is generated by discharging a capacitor. This feature that has the advantage that a very high welding current can be generated for a short period of time at a comparatively low cost.
Picking up the sphere by use of the first electrode can be achieved by way of a suction device that is provided on the first electrode or is integrated in the first electrode. For this purpose, a face side of the first electrode can have a recess, into which the sphere is sucked by way of the suction device such that at least one side of the sphere that is to be welded still protrudes from the recess. The suction device can be arranged on the first electrode or can be at least partially or totally integrated into the first electrode. The recess can be configured, for example, in the form of a hemisphere, conically, or in any other manner in the form of a cup. What is important is that the recess be configured in such a way that when the sphere is sucked up, the sphere is positioned in a defined manner, i.e. exactly with respect to the first electrode. Preferably, the sphere touches an inner side of the recess along a small circle of the sphere.
In order to automate the picking up of the sphere by use of the first electrode, a feed device can be used. It can be provided that the sphere is held initially at the feed device and then transported into the area of the face side of the first electrode by way of the feed device. As soon as the sphere is situated in the “suction area” of the first electrode, the sphere can be sucked in by the first electrode and, in so doing, can be delivered to the first electrode.
The feed device can be designed as a pivotable feed device. The sphere can be brought into the suction area or, more specifically into the area of the face side of the first electrode, by pivoting the feed device about a pivot axis. Similarly, the feed device can also be provided with a suction device for sucking in and holding the sphere that is to be transported. For this purpose the feed device can have a recess, into which the sphere is sucked, so that the sphere protrudes at least so far out of the recess that it can be sucked in by the suction device of the first electrode.
The above-described method lends itself especially well to welding metal spheres onto the metal sheet of motor vehicle bodies. The spheres can be, for example, steel spheres or aluminum spheres; or the spheres can be spheres made of a different metal or, more specifically, a metal alloy. The above-described method lends itself especially well to an automated process by use of a robot.
Other objects, advantages and novel features of the present invention will become apparent from the following detailed description of one or more preferred embodiments when considered in conjunction with the accompanying drawings.